CRTH2 is a G protein-coupled chemoattractant receptor expressed on Th2 cells, eosinophils, and basophils (Nagata et al., J. Immunol. 1999, 162, 1278-1286; Hirai et al., J. Exp. Med., 2001, 193, 255-261). Prostaglandin D2 (PGD2), the major inflammatory mediator produced from mast cells, is a natural ligand for CRTH2. Recently, it has been shown that the activation of CRTH2 by PGD2 induces the migration and activation of Th2 cells and eosinophils, suggesting that CRTH2 may play a pro-inflammatory role in allergic diseases (Hirai et al., J. Exp. Med. 2001, 193, 255-261; Gervais et al., J. Allergy Clin. Immunol. 2001, 108, 982-988). It has also been shown that, in atopic dermatitis patients, there is an increase in circulating T cells expressing CRTH2, which correlates with the severity of the disease (Cosmi et al., Eur. J. Immunol., 2000, 30, 2972-2979; Iwazaki et al., J. Investigative Dermatology, 2002, 119, 609-616). The role of PGD2 in the initiation and maintenance of allergic inflammation has further been demonstrated in mouse models of asthma by showing that overproduction of PGD2 in vivo by PGD2 synthase exacerbates airway inflammation (Fujitani et al., J. Immunol. 2002, 168, 443-449). Therefore, CRTH2 antagonists are potentially useful for the treatment of CRTH2-mediated disorders or diseases, such as allergic rhinitis, allergic asthma, bronchoconstriction, atopic dermatitis, or systemic inflammatory disorders.